This invention relates to a periscope usable in a land military vehicle to provide increased visibility over hills or obstacles that would otherwise shield enemy targets from view. The periscope has the following general features:
1. variable height adjustment for retraction to a concealed position or raising to required viewing height.
2. a fixed eyepiece location for all periscope heights and viewing directions, whereby the tank commander can remain seated in one stationary position.
3. a constant fixed optical system path length in all periscope positions for maintaining a continuous sharp focus on the target scene.
4. inertial stabilization of the sighting head at the upper end of the periscope to minimize jitter of the image while the vehicle is moving over rough terrain.
5. reticle plate location in the sighting head at the upper end of the periscope for maintaining crosshair positionment on the optical axis in spite of flexure movements of the periscope mast structure.
6. a relatively large periscope extension length for a given height vehicle.